How long does a boiler last?
Updated August 2026
A boiler lasts 15–30 years, a wide spread that comes down almost entirely to type. An old cast-iron boiler is a tank: the heavy sections resist corrosion, and many run 30 years or more, some past 40. A modern high-efficiency condensing boiler, the 90%+ AFUE kind that wrings extra heat from the flue gas, trades that longevity for efficiency and typically lasts 10–15 years, because its aluminum or stainless heat exchanger and its electronics are more delicate. Water quality is the deciding factor either way: dirty, untreated system water scales and corrodes the exchanger from the inside, and a boiler starved of annual service ages fastest of all.
Lifespan by type and situation
| Type or situation | Typical lifespan | Why |
|---|---|---|
| Cast-iron boiler | 30+ years | Heavy sections resist corrosion; some reach 40 |
| Standard steel or copper-tube boiler | 15–25 years | The common middle of the range |
| High-efficiency condensing boiler | 10–15 years | Efficient, but the exchanger and electronics wear sooner |
| Hard or untreated system water | Cut 3–8 years | Scale and corrosion attack the heat exchanger |
| Serviced yearly, treated water | Top of the range | Clean water and annual service buy the extra decade |
| Oversized, short-cycling | Cut 3–5 years | Frequent firing stresses the exchanger and controls |
Signs yours is near the end
- Rusty water or sediment when you drain a little from the boiler, a sign the exchanger is corroding
- Pressure that will not hold steady, or a relief valve that weeps or opens repeatedly
- Cold spots in radiators, or zones that used to heat evenly
- Rumbling, kettling, or banging as scale traps steam against the exchanger
- A gas bill creeping up while the thermostat stays put
How to add years
Clean water and steady pressure are what a boiler lives on. Have it serviced once a year so a tech can check the combustion, flush or treat the system water, and bleed trapped air from the radiators. Check the pressure yourself every month or two and keep it in the normal 12–15 psi band, since a system running dry or overpressured stresses the exchanger and the relief valve. Add or refresh the corrosion inhibitor whenever a pro drains the loop, and walk the boiler maintenance checklist each fall. Once a boiler leaks from its body or faces a heat-exchanger repair, price a replacement rather than patching it.
What it costs to replace: plan on $6,000–11,000 installed. Replacing on your own schedule, before it fails, is almost always cheaper than the emergency version. The home maintenance cost calculator helps you set the money aside before it comes due.
OnOtto tracks your boiler service visits age and service history, and warns you before end of life instead of after the flood.
Track your home's systems, free for 30 daysFrequently asked questions
Why do old cast-iron boilers last so long?
Mass and simplicity. A cast-iron boiler's thick sections take decades of corrosion to eat through, and the older designs have few electronics to fail, so many keep heating for 30 years and beyond. The trade-off is efficiency: a 30-year-old cast-iron unit may run at 60–70% AFUE, wasting a third of its fuel up the flue, while a modern condensing boiler hits 90%+. So a working antique can be worth keeping until it leaks, but its fuel bills quietly argue for an upgrade.
Do high-efficiency boilers really last only 10 to 15 years?
Often, yes, and it surprises people. Condensing boilers earn their 90%+ efficiency by pulling so much heat from the exhaust that the flue gas condenses into a mild acid, which, along with more electronics and a delicate aluminum or stainless exchanger, gives them a 10–15 year life against a cast-iron unit's 30. Good ones last longer with clean, treated water and yearly service; neglected ones fail sooner. The fuel savings usually still come out ahead, but budget for replacement on a shorter cycle.
What kills a boiler fastest?
Bad water and skipped service. Untreated or oxygen-rich system water scales and corrodes the heat exchanger from the inside, and that internal damage is what usually ends a boiler's life. Low or wildly swinging pressure, air trapped in the loop, and a unit oversized so it short-cycles all pile on. The fix is cheap by comparison: an annual service, a corrosion inhibitor in the loop, and holding pressure around 12–15 psi can add many years to any boiler.